Summary: It is well established that HTLV-I is the etiologic agent for a number of diseases, including adult T-cell leukemia and a neurological disorder called HAM/TSP. In addition, accumulating evidence suggests that HTLV-II may be involved in disease, as well. These disease correlations and the fact that HTLV-I and HTLV-II can be transmitted by transfusion have led to the recommendation that blood donors be screened for evidence of HTLV-I and HTLV-II infection. This project seeks to determine if current methods for screening blood donors are sufficient to detect both HTLV-I and HTLV-II infections. In one area, we are extending a study that is examining the frequency of HTLV-I tax sequences in normal blood donors. This study seeks to determine the reproducibility of claims that these sequences were detected in up to 11% of normal healthy random blood donors who were negative on conventional HTLV-I/HTLV-II screening tests. These studies are a follow-up to a CBER organized study in which it was determined that the original findings could not be reproduced in a blood donor cohort from the Washington, DC/Baltimore, MD area. Specimens are now being analyzed from blood donors in the New York City area, in collaboration with the CDC and with participation from the laboratory at New York University which made the original observations. In a second area, we have developed an assay to detect the presence of antibodies to HTLV-I tax and are in the process characterizing its specificity and sensitivity. This peptide-based enzyme immunoassay is being used to screen specimens from normal blood donors and HTLV-I-infected individuals for anti-tax antibodies.